Fast transient A-type K+ currents (IA), such as the subthreshold-activating somato-dendritic A-type K+ currents in neurons (ISA) and the fast transient outward K+ current in cardiac ventricular myocytes (Ito) are essential for the proper functioning of the brain and the heart. During pathophysiological conditions (e.g. ischemia in the heart and during the occurrence of stroke in brain) abnormalities in these currents contribute to the abnormalities associated with these disease conditions. This project addresses the molecular nature of the ion channels responsible for the generation of these currents. It seeks to establish the molecular composition of these channels and to elucidate the physiological significance of the identified components. Progress has been made in elucidating the molecular composition of the channels mediating the ISA and the Ito, and two key components, Kv4 pore-forming subunits and KCHIP associated proteins, have been identified. However, the kinetics of ISA channels in many neurons is faster than that of channels composed of Kv4 and KCHIP proteins. Evidence has been recently obtained for the presence in brain mRNA of transcripts encoding a factor (termed KAF), probably a novel associated subunit, which accelerates the kinetics of Kv4 channels. Moreover, a novel Kv4 channel associated protein (DPPX) has been identified utilizing biochemical methods, and evidence that this protein is responsible for KAF activity has been obtained. The goal of this project is to test the hypothesis that DPPX is an important component of Kv4 channels in many neurons and contributes to the properties and diversity of native A-type K+ channels. Aim 1 will investigate the effects of DPPX on Kv4 channel function in heterologous expression systems. Aim 2 will investigate where and when DPPX proteins are expressed in brain and their relationship to the other known components of Kv4 channels utilizing in-situ hybridization and immunohistochemistry. Aim 3 will investigate more directly the physiological significance of DPPX proteins in neurons utilizing gene targeting and antisense technology. [unreadable] [unreadable]